Friction elements and method of making same



Patented June '24, 1930 uni-TED STATES PATENT orrlcr.

J KOVAK, O1 BBIDGEPOR'I, CONNECTICUT, ASSIGNOB, BY IESNE ASSIGN- m me,1'0 BAYBESTOS-IANHATTAN, INC-, A. CORPORATION OF NEW JERSEY,

rnrcrron ummirrsami reunion or Maxine sum 11o Drawing. Application filedJanuary 28, 1924, Serial No. 688,108. Renewed December 2, 1929.

This present invention relates to friction elements and process ofmaking same, said frictioni'materials comprising clutch facings,frictionrblocks', and the like formed from a 5 base ofasbestos pulp orwoven asbestos tape saturated with an organic drying oil binder, withoutthe aid of any solvent or'carrier for the binder.

The method generally employed at the present time in the manufacture ofclutch facings and other frictio elementswhen' using an asbestos pulp bV saturated with an organic drying oil binder is essentially as follows?Asbestos sheeting in the desired thickness and form, is impregnated atroom temperature with a solution of the liquid binder, for instance,linseed oil, in a suitable solvent, such as gasoline or the like. Afterimpregnation, the solvent is removed by heating the impregnated asbestosin an oven, which heating is continued, to dry and harden the oil.

Ithas been found by those skilled in the art,

that in employing a solvent, the proportion of binder-oil to solvent maynot safely be raised above 3 to 1 without encountering a glazing of thesurface due to exudation of binder oil from the interior portions of theimpregnated pulp to the outside with resultant hardening there, whichthereupon effectually seals the interior from the access of air neededfor satisfactory drying of the binder oil, and so .prolongs .to adisproportionate time the eating period essential for the complete haening of all the binder.

Thus, for example, it was found that a clutch facing which normallycured' in thirty hours, when impregnated with a slightly heavy oilsolution, formed a skin of dried oil on its surface, and did not curecompletely in sixty hours. It-'is, however,

quite possible to manipulate the cure of a clutch facing such asdescribed above so asto prevent the formation of a glaze by means ofa'long'drying at a low temperature previous: to exposure to the normalhardening temperature. This would be extremely ob-,

jectionable in practice duexto the care necessary in regulation oftemperatures, and-the prolonged time of cure. It will be seen,

illustration of this procedure, which I have therefore, that'not only isthe loss of a considerable amount of solvent necessary, but that slightchanges in solution strength have serious effects on the cure. Anotherdisad-' vantage is that due to the use of a solvent, the pores, thou hcompletely filled with the impregnating uid at first are afterwardspartially emptied dueto the volatilization of a the solvent on heating.This results in less compactness, solidity and strength than where thepores are more completely filled, as in the process to be describedbelow.

Another disadvantage attachable to this method of saturation and curelies in the fact-that it' is practically impossible to cure a drying.oil in an asbestos pulp base uniformly-hard from center to outside evenwhen there is no decided glazing in a reasonable length of time such as24 to hours, in any thickness greater than inch, dueto the gradualsealing, of the surface pores in a cure which must commence from theoutside and proceed inwards. By the methods described below the wholethickness is evenly cured to beginwith, and

there is no sealing of the interior portions.

I have cured asbestos ulp or wood fibre pulp in thicknesses as hlghasone inch, and believe the method capable of use in curing still greaterthicknesses. Y

My invention comprises essentially the impregnation of the asbestos basesuch as asbestos pulp, or woven yarn with an organic drying oil,thepar'tial hardening of the oil by heat treatment under pressure withpartial or complete exclusion of air, or in a non-oxidizing atmosphere,withor without pressure and the final hardening of the oil by heattreatment in' an oxidizing atmosphere, with or without pressure. Thelast operation may, of course, be omitted if partial hardening of theoil is sufiicient for the purpose desired. A

The following description exemplifies one practiced in the fabricationof friction elements for use in automobile clutches: Annular ring blanksof approximately the desired dimensions are 'stampedout from asbestosmill board by the use of a die and die cure, and is not essential to theprocess. A

coating of fine graphite may then be applied to the rings and they arestacked in any desired number, the pack being held together .between twoiron plates connected by a bolt.

The entire pack may then be subjected to a temperature of 400 F. forsay, 4 hours. On removal from the oven, the pack is ale lowed to cooland the rings are then separated. At this pointthe oil has beenpartially hardened, and the rings are firm, and fairly strong, but notyet sufliciently hard for satisfactory use in a clutch. They may be thenhung on spindles and baked in the open in an oven heated to 325 F. for aperiod sufficient to bring the hardness up to 14 Brinnell. This may takefrom six to twenty hours, depending on the thickness of the rings. Afterthe final cure is complete, the rings may be sanded down to size and thegraphite removed from the surface in the same operation. The edges maybe brushed, or if necessary, turned down to size in a lathe.. Thefinished-ring is a product superior to any made with the aid of asolvent as carrier for the drying oil, in

density, toughness, flexibility, resistance toshock, and general'machineability.

The foregoing illustration is only one of a large number of applicationsof this process to the art of friction element manufacture. I have usedit for friction blocks up to one inch in thickness. The methodforproducing brake linings with an asbestos pulp base and drying oil binderis a simple operation, the resultant product being very durable. Coneclutch facings have substantially the same characteristics as the brakehning. Insulation sheeting made with a drying oil and any vegetable,mineral or animal fibre can be made up to a thickness of one inchwithout lamination. Also as has been shown above, this method provides ameans for the hardening of a drying oil in fibrous base of much greaterthickness than has been practical heretofore, by the use of a solvent asvehicle for carrying the oil.

The invention may be applied to thick woven fabrics with equally goodresults,

and brake lining, clutch facings and other products with woven fibrousbase show the same advantageous characteristics that areevidenced inpulp base materials.

The drying oil used in my invention may I ing oils such as linseed,China wood, perilla,

etc.,are the best for the ends desired, but I have found that many socalled non-drying or semi-drying oils such as palm, corn, rapeseed,etc., also give very satisfactory'results by the use of the methodspecified.

Oils or combinations of oils which do not have a marked tendency toglaze, especially China wood oil and mixtures of it with other oils whenused as a saturant as heretofore described, may be partially hardened,if desired, in a substantially non-oxidizing atmosphere such as carbondioxide, nitrogen, flue gas, ammonia, etc., at an elevated temperature,say from 300 to 500 15. with or Without pressure, depending on thecharacter of the oil. Oils with marked tendency to glaze, such aslinseed when used as a saturant, as heretofore described may bepreferably hardened in an inert gas under pneumatic pressure, whileChina wood oil which has only slight glazing tendency, may be hardenedwith the gas at atmospheric pressure. v

I claim as my invention:

1. Steps in a process of producing friction elements consisting inimpregnating a noncombustible fibrous base with saturant, partiallyhardening the saturant by subjecting the impregnated fibrous base toheat under pressure with partial or complete exclusion ofair, andfinally hardening the saturant in the impregnated base by subjecting thebase to'hcat in an oxidizing atmosphere.

2. Steps in a process of producing friction elements consisting inimpregnating a non-combustible fibrous base with a saturant, partiallyhardening the saturant by subjecting the impregnated base to heat tionelements consisting in impregnating a non-combustible fibrous base witha saturant, partially hardening -the saturant by subjecting theimpregnated base to heat in a non-oxidizing atmosphere, and finallyhardening the saturant in the impregnated base by subjecting said baseto heat and an oxidizing atmosphere under pressure.

IZADOR J. NOVAK.

